1. Field of the Invention
The present invention relates to the nose of a boom; and more particularly, a multi-position low profile boom nose.
2. Description of Related Art
The nose of a boom, multi-section or otherwise, is typically a welded steel structure that houses and provides support for one or more sheaves mounted to a shaft, and is used to redirect a lifting or load line around the point end of the boom to the load. Boom nose sheaves may be mounted to one single shaft at one location, but often there is an upper sheave assembly and a lower sheave assembly. The upper or primary sheave directs the load or lifting line around the end of the boom to a lower or secondary sheave assembly (i.e., lower boom nose sheave, auxiliary boom nose sheave, boom extension sheave). The secondary sheave assembly is necessary to accommodate multiple parts of line required when loads, which are greater than the allowable limit for one or two parts of line, are lifted. If no loads will be lifted that exceed the allowable limit for two parts of line, then one sheave location is sufficient.
When multiple parts of line are required, a hookblock is used to lift the load. A hookblock is a lifting device consisting of one or more sheaves enclosed in a steel housing with a hook at the bottom used for grabbing the load. For two parts of line, the wire rope must pass over the lower sheave on the boom nose, continue down around the hookblock sheave, and then return back again to the boom nose where it is attached to a dead end lug. For three or more parts of line, an appropriate number of lower boom nose sheaves and hookblock sheaves are required, and the load line is reeved back and forth between the two until the number of parts of line is obtained.
When lifting loads using multiple parts of line at high boom angles, the return lines from the hookblock to the lower boom nose sheaves must clear the bottom of the boom sections. This requires that the boom nose extend below the bottom of the boom to accommodate the necessary location of the lower boom nose sheaves. Thus, the overall height of the boom nose becomes greater than desirable as it reduces the height a load may be lifted.
A compact boom nose is an important feature when lifting loads in confined areas where accessibility is limited. However, it is also desirable that the maximum lifting capability not be compromised.